CN101031852B - Process device with diagnostic notification - Google Patents

Abstract

A process device (12) for coupling to a two wire process control loop (18) includes diagnostic circuitry (64) configured to identify a fault or a reduction in performance level or to provide a prediction of a future fault or reduction in performance level. An output coupled to the two wire process control loop (18) is configured to provide an analog output on the loop (18) related to the output from the diagnostic circuitry (64), wherein the analog current level has more than two values, each of the values being indicative of a different diagnostic condition. The invention also provides a method.

Description

Process device with diagnostic notification

technical field

The invention relates to a process plant of the type used in industrial processes. More specifically, the present invention relates to the communication of diagnostic information.

Background technique

Field devices such as process controllers, monitors and transmitters are used in the process control industry to remotely control, monitor and sense process variables. For example, process variables may be sent by transmitters to a control room for use in controlling the process and for providing information to the controller regarding the operation of the process. For example, information about the pressure of a process fluid can be communicated to a control room and used to control a process such as a petroleum refinery.

通信协议。

协议和其它这样的协议典型地包括一组命令或指令，所述一组命令或指令可以被发送到变送器以引起想要的响应，例如变送器控制或询问。A typical prior art technique for communicating eg a process variable involves controlling the amount of power flowing through a process control loop. Current is supplied from a current source in the control room, and the transmitter controls the current from its location in the field. For example, a 4mA signal can be used to represent a zero reading (or what is called a starting point reading), and a 20mA signal can be used to represent a full scale reading. More recently, transmitters have employed digital circuitry that communicates with the control room using digital signals superimposed on the analog current signal flowing through the process control loop. An example of this technique is developed by the Rosemount Corporation

letter of agreement.

Protocols and other such protocols typically include a set of commands or instructions that can be sent to the transmitter to cause a desired response, such as transmitter control or interrogation.

协议和Ethernet。在一些构造中，可以使用两个、三个、四个或任何数量的电线连接到过程装置，包括例如RF(射频)的非物理连接。Fieldbus is a communication protocol proposed by the Fieldbus Foundation and is used to define a communication layer or communication protocol for transferring information on a process control loop. In the Fieldbus protocol, the current flowing through the loop is not used to transmit analog signals. Instead, all information is transmitted digitally by modulating the current flowing in the process control loop. Furthermore, the Fieldbus standard, also known as Profibus, allows transmitters to be constructed in a multidrop configuration in which more than one transmitter is connected to the same process control loop. Other communication protocols include

Protocol and Ethernet. In some configurations, two, three, four, or any number of wires may be used to connect to the process device, including non-physical connections such as RF (radio frequency).

Some process transmitters may also transmit an alarm signal that may provide an indication that a process variable measurement is saturated (ie, a process upset). One type of alarm signal fixes the current through the loop at a predetermined level or outside a predetermined threshold. For example, one type of alarm signal is a current level that is greater than 21 mA or less than 3.8 mA and can be used to signal "high alarm" and "low alarm", respectively. An alarm signal can be sent by the transmitter when an alarm condition occurs.

Contents of the invention

A process device for connection to a two-wire process control loop includes a diagnostic circuit configured to diagnose operation of the process device. An output connected to the two-wire process control loop is configured to provide an output on the loop related to a diagnostic condition, wherein the analog current level has more than two values, each said value indicating a different diagnostic condition. The invention also proposes a method and an interface circuit.

Description of drawings

1 is a schematic diagram illustrating a process control system including process devices connected to a process control loop;

Figure 2 is a perspective view illustrating the interior of the process device in Figure 1;

Figure 3 is a simplified block diagram of the circuitry in the process device; and

4 is a simplified block diagram illustrating interface circuitry for connecting a process device to control room circuitry.

Detailed ways

The present invention proposes a method and apparatus for announcing diagnostic information by using an analog signal transmitted over a loop using a two-wire process control. Typically, two-wire process control loops employ a 4 to 20 milliampere signal representing the process variable. However, in many instances the process device is also capable of generating diagnostic information. The present invention relates to techniques for communicating such information.

There is an ever-increasing demand that diagnostic capabilities should be included in process installations. In particular, there is a need for the ability to provide predictive diagnostics that yield an indication of the likelihood of future failures. Awareness of impending failure allows maintenance actions to be scheduled and implemented before eventual failure of the device occurs. This results in higher plant utilization and increased efficiency.

通信标准和/或4至20毫安培标准。One obstacle to implementing diagnostic capabilities into process devices is the method used to communicate the diagnostic results. New process devices can provide communication technology by means of which diagnostic information can be sent to other devices or locations, for example to a control room. Examples of these communication technologies include the use of Fieldbus, Profibus, Modbus, Internet, Ethernet, RS-485, wireless communication technologies and others. These techniques provide process devices with the ability to initiate messaging and transmit diagnostic information. However, much of the process control industry continues to use older communication technologies such as

communication standard and/or 4 to 20 mA standard.

通信轮询技术询问装置。过程装置然后可以使用

数字通信协议用数字通信诊断结果。Currently, in some configurations, alarm values outside the normal 4 to 20 milliampere operating current range are used to signal an alarm condition. Another technique is to use

Communication polling technology interrogation device. The process device can then use the

The digital communication protocol communicates diagnostic results digitally.

主机、且构造成接收诊断信息的装置。此外，在存在

主机的装置中，与诊断相关的轮询相关联的额外通信量可能会不利地影响系统的带宽。If the 4 to 20 milliampere loop current is used to convey the alarm signal, then the process variable cannot be sent to the clock because the analog output function changes from representing the process variable to representing diagnostic information. Furthermore, this technique is not particularly suitable for predictive diagnostics because the alarm signal is only sent after the alarm condition has occurred. Furthermore, alarms cannot be sent in a continuous manner without loss of process variables. Although information can be based on communication standard to communicate from process devices, this method is still limited to existing

host and configured to receive diagnostic information. In addition, in the presence of

In the host's device, the extra traffic associated with diagnostic-related polling may adversely affect the bandwidth of the system.

The present invention presents a method and apparatus for transmitting diagnostic information from a process device in the form of an analog current carried on a two-wire process control loop. The analog output can be in any number of forms. In one example, the current level is set or controlled on the process control loop, indicates a diagnostic condition, and the current level has more than two values. Specific current levels can be mapped to specific diagnostic conditions to provide diagnostic information. Similarly, further process devices may be connected to the process device providing diagnostics. This additional process device can receive a digital representation of the diagnostic condition and can convert the digital representation to an analog current signal of 4 to 20 milliamps. This 4 to 20 mA current signal can be used with existing control room installations. Such a device that can convert a digital process variable to a 4 to 20 milliampere analog signal is shown and in U.S. Patent No. 5,650,777, issued July 22, 1997 (the title of the patent is CONVERSION CIRCUIT FORPROCESS CONTROL SYSTEM) get described.

When used to provide predictive diagnostics, the current level in the loop can be controlled to represent changes in diagnostic results. For example, a progressively deteriorating composition or other diagnostic indication may be indicated by gradually increasing (or decreasing) the analog value along a predetermined profile. When the simulated values exceed predetermined thresholds, equipment in the control room can provide an indication that a fault is imminent. Similarly, the host system monitoring the diagnostic analog current output may be configured to implement an exception handling (or exception handling) policy based on user-defined thresholds. If the simulated value exceeds a threshold, a specific control configuration can be implemented. This can be used to safely stop process operation. In another example, the process device provides a second analog output in addition to the analog process variable output. Analog outputs may also be generated by remote input/output devices such as device hubs or similar devices. In another example, rather than providing a single estimated current level to represent a diagnostic condition, a process device may provide a particular pattern of current levels to represent a particular process condition.

This configuration allows existing control room equipment to take advantage of the diagnostic capabilities in the process installation. Existing control room equipment can be easily programmed to monitor analog current levels and take desired steps, such as signaling an alarm if a threshold is exceeded. The present invention can be configured to allow simultaneous acquisition of measured process variables and diagnostic results. In addition, an analog output, which may take on multiple values, may be used to provide an indication on a continuum of diagnostic results, eg, diagnostic results representing proper functioning of a device or component. This provides the control room with more information than simply providing estimated alarm values. Furthermore, this configuration does not require additional polling of devices or other complex infrastructure.

协议运行的一个实施例中，回路18可以传送代表传感的过程变量的电流I。例如，传感器21可以传感用于在回路18上传送的过程变量。另外，协议允许数字信号叠加在通过回路18的电流上，从而数字信息可以被发送到变送器12或从变送器12接收。在一个实施例中，回路18中输送的电流I不是代表过程变量，而是代表诊断条件。例如，电流I可以在4毫安培与20毫安培之间，且代表由过程装置12中的电路确定的特定的诊断条件。在另一示例中，电流I可以被设定成任何数量的值(包括在连续范围内的任何数值)，所述任何数量的值代表诊断确定(diagnostic determination)。例如，4毫安培电流可以代表特定诊断条件，而5毫安培可以代表另一诊断条件等。如果使用连续的值，电流I可以在两个端点之间值域内，且电流I值可以代表连续变化的诊断条件。在另一示例中，电流I可以被设定为代表诊断条件的三个或更多不同的电流电平。在控制室20内的电路可以监视回路18中的输送的电流电平I。例如，传统的控制室构件可以监视电流电平、并在电流电平I超出或达到特定阈值的情况下发出报警或提供其它输出。FIG. 1 is a schematic diagram of a process control system 10 including a transmitter 12 connected to a process piping 16 . The transmission 12 is connected to a two-wire process control loop 18 that is configured according to a desired protocol such as Standard or 4 to 20mA analog standard operation. However, the invention is not limited to these standard or two-wire configurations. A two-wire process control loop 18 extends between the transmitter 12 and the control room 20 . In which loop 18 according to

In one embodiment of the protocol operation, the loop 18 may carry a current I representative of the sensed process variable. For example, sensor 21 may sense a process variable for communication on loop 18 . in addition, The protocol allows digital signals to be superimposed on the current passing through loop 18 so that digital information can be sent to or received from transmitter 12 . In one embodiment, the current I delivered in loop 18 is not representative of a process variable, but rather a diagnostic condition. For example, current I may be between 4 milliamperes and 20 milliamps and represent a specific diagnostic condition determined by circuitry in process device 12 . In another example, current I may be set to any number of values (including any value within a continuous range) that represent a diagnostic determination. For example, 4 milliamps of current may represent a certain diagnostic condition, while 5 milliamps may represent another diagnostic condition, and so on. If a continuous value is used, the current I can range in value between the two endpoints, and the current I value can represent a continuously varying diagnostic condition. In another example, current I may be set to three or more different current levels representative of diagnostic conditions. Circuitry within the control room 20 can monitor the delivered current level I in the loop 18 . For example, conventional control room components may monitor current levels and issue an alarm or provide other output if current level I exceeds or reaches a certain threshold.

FIG. 1 also illustrates an optional second process control loop 26 . In embodiments employing process control loop 26 , process control loop 18 may communicate a standard process variable, such as one measured using process variable sensor 21 . The second process variable control loop 26 may deliver a current _ID representing diagnostic information in a manner similar to that discussed above. However, other delivery techniques may also be used. This configuration allows the process control loop 18 to continuously deliver the primary process variable while providing diagnostic information on the secondary process control loop 26 . In one configuration, the second process control loop 26 conveys digital information related to the diagnostic condition.

FIG. 2 is a perspective view of transmitter 12 showing one exemplary configuration of circuit blocks carried therein. In the exemplary embodiment, transmitter 12 includes a signature module 40 connected to a sensing module 42 . The sensing module 42 is connected to the process piping 16 (shown in FIG. 1 ) by a header process connection 44 .

The signature module 40 includes a signature module electronics circuit 50 connected to a sensing module electronics circuit 52 carried within the sensing module 42 . Typically, sensing module electronics 52 is connected to a process variable sensor, such as sensor 21 shown in FIG. 1 , for sensing a process variable related to process operation. Feature module electronics 50 includes output circuitry 60 , process variable circuitry 62 , and diagnostic circuitry 64 . Circuitry 60 , 62 , and 64 may be implemented in hardware, software, or a combination of hardware and software, and may be located anywhere within transmitter 12 . Furthermore, the various circuits 60, 62, and 64 may share components.

In operation, output circuit 60 controls the value of current I flowing through loop 18 to represent, for example, a measured process variable or a diagnostic condition. This can be used to monitor or control industrial process operations. In some applications, output circuit 60 is also used to provide power to circuitry within transmitter 12 generated using power received through loop 18 and/or loop 26 . If the second loop 26 is used, the output circuit 60 is also configured to control the current level. The output circuit 60 may consist of a single output circuit or a plurality of output circuits.

According to one aspect of the present invention, diagnostic circuitry 64 performs any type of diagnostic for detecting or predicting failure modes of transmitter 12 and/or other process devices or components. Diagnostic circuit 64 enables output circuit 60 , and output circuit 60 places a diagnostic current level on loop 18 or 26 . For example, output circuit 60 may set the loop current to a predetermined value. In a 4 to 20 milliampere current loop, current I may be set by output circuit 60 to a value less than 3.8 mA or approximately 21 mA in one example to send an alarm on loop 18 or 26 . These current levels are referred to as "low alarm" and "high alarm", respectively. However, the current level can be set to any level if desired. For example, as discussed above, the current may be set to more than three different levels, each of the different levels indicative of a diagnostic condition. In another example, the current level may be set to a value between 4 milliamps and 20 milliamps to represent a diagnostic condition. Continuous values of current levels may also be used to provide an output indicative of continuous diagnostic conditions. Additionally, the current level may vary over time in a predetermined pattern to indicate a particular diagnostic condition.

FIG. 3 is a simplified block diagram of transmitter 12 . As shown in FIG. 3 , transmitter 12 includes measurement circuitry 62 connected to process variable sensor 21 . Measurement circuitry 62 may be included on sensor module circuit electronics 52 shown in FIG. 2 . Circuit 60 is connected to measurement circuit 62 and is configured for sending (and in some embodiments, receiving) information on process control loop 18 and optional loop 26 . The output circuit 60 includes a first loop output circuit 60A and an optional second loop output circuit 60B. However, circuits 60A and 60B may be constructed according to other embodiments. Measurement circuitry 62 is configured to provide initial processing of the process variable sensed by sensor 21 . The implementation of measurement circuitry 62 often includes a microprocessor. The microprocessor may also be used to perform other circuit functions shown in the device.

In normal operation, the process variable sensed by sensor 21 is converted to an analog current level or a digital signal for delivery on process control loop 18 using output circuit 60 . However, when a diagnostic condition is sensed by diagnostic circuit 64, output circuit 60 is configured to provide a current level output on loop 18 or 26 at a predetermined current level, eg, above or below a threshold level. The output circuits 60A, 60B may be connected in series or in parallel with other circuits. Other configurations may also be used. In some embodiments, the second output circuit 60B is configured to switch off or otherwise disconnect or de-energize when not in use, inactive or reduced in power.

FIG. 4 is a simplified block diagram of a process control system 100 that includes a process device 102 , interface circuitry 104 , and control room circuitry 106 . Process devices 102 are shown connected to a single process control loop 110 . This process control loop is configured to carry more than one type of information. For example, the primary process variable can be represented by the current I carried on the loop 110 and other information can be digitally modulated onto the loop 110 . In another example, all information is digitally modulated onto the control loop 110 .

Control loop 110 is connected to interface circuit 104 , which is connected to control room circuit 106 through first process control loop 112 and second process loop 114 . Interface circuit 104 receives more than one type of information from process device 102 via loop 100 . At least one type of information received by interface circuit 104 is related to diagnostics. Interface circuit 104 _is configured to provide a current level _ID on loop 114 that correlates with received diagnostic information. The current level is received by the control room circuit 106 so that the control room circuit 106 receives diagnostic information. Interface circuit 104 may be connected to other process control loops such as loop 112 shown carrying IP _PV . For example, the current level in loop 112 may represent a process variable received from process device 102 . In some configurations, the interface circuit 104 provides diagnostic information only to the control room circuit 106 . In such a configuration, process variable information may be provided, for example, over a separate loop such as loop 110 .

Although a single process device 102 is shown connected to loop 110 and a single loop 110 is shown connected as an input to interface circuit 104 , any number of process devices and/or process control loops may be connected to interface circuit 104 . Similarly, interface circuit 104 may control electrical current or digital signals carried in any number of process control loops. Additionally, diagnostics may be performed by circuitry associated with interface circuitry 104, eg, using input data received from the loop.

Using the configuration shown in FIG. 4, the control room circuit 106 may operate according to conventional techniques. For example, the control room circuitry 106 may simply monitor the current level _ID carried within the loop 114 and issue an alarm or other output if the current level exceeds a predetermined threshold. The interface circuit 104 allows information from the process device to be obtained in a conventional form through the control circuit 106, as opposed to requiring the circuit 106 to be upgraded according to recent standards. The interface circuitry may map diagnostic information to specific current levels based on specific diagnostic conditions. The interface circuit may provide the current level as a continuous or semi-continuous value, or may provide a pattern of current level output to indicate a diagnostic condition. The interface circuitry may be physically located in any suitable location within the system 100, such as inside the control room, outside the control room in a non-hazardous area, or in a hazardous area where the circuitry must meet inherent safety standards. Loop interface circuit 104 may be powered entirely from one or more process control loops connected to circuit 104 . In such configurations, however, the interface circuitry would require sufficient power to power the process control loop 110 and (in some configurations) the process device 102 . Alternatively, a separate power supply may be used to power interface circuit 104 .

As used herein, any process device may generate diagnostic information including a controller, positioner, process variable measurement device, interface circuit, or other device connected to a process control loop. Diagnostic information may be generated locally and/or based on data received from other sources (eg, over a process control loop). The diagnostic information may be any type of diagnostic information, including diagnostic information relating to the occurrence of an immediate event, or predictive information relating to the likelihood of a future event occurring. Any desired diagnostic technique can be used with the present invention.

或其它通信协议(所述通信协议通过控制过程控制回路中的电流传送与过程有关的信息)运行的回路。本发明在安全仪表系统(SIS)构造中特别有用，所述安全仪表系统构造为过程控制回路提供附加的安全层(safety layer)。通过提供附加的诊断通知能力，本发明可以提供改进过程装置的安全整体性水平(SIL)等级的技术。在一个示例中，报警电平(或报警级；alarm levels)是诊断条件的通知。Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will understand that changes may be made in form and detail without departing from the spirit and scope of the invention. The above description illustrates the invention with an example configuration, but any suitable process control loop may be used, such as a 4 to 20 mA, 2, 3 or 4 wire loop, a multipoint loop, and according to Fieldbus, Profibus,

or other communication protocols that communicate process-related information by controlling the electrical current in the process control loop. The invention is particularly useful in safety instrumented system (SIS) configurations that provide an additional safety layer for process control loops. By providing additional diagnostic notification capabilities, the present invention may provide techniques for improving the Safety Integrity Level (SIL) rating of a process device. In one example, alarm levels (or alarm levels; alarm levels) are notifications of diagnostic conditions.

Claims (46)

1. A process device for connection to a two-wire process control loop comprising: diagnostic circuitry configured to diagnose operation of a process device or process; an output configured to connect to a two-wire process control loop configured to provide an analog current output on the loop, wherein the analog current level has a first value indicative of a first diagnostic condition, A second value indicative of the second diagnostic condition and a third value indicative of the third diagnostic condition. 2. The process device of claim 1, wherein the loop analog current output is between 4 mA and 20 mA. 3. The process device of claim 1, wherein the loop analog current output is indicative of predicted diagnostic information. 4. The process device of claim 1, wherein the process device comprises a process variable transmitter. 5. The process device of claim 1, wherein the process device comprises a process controller. 6. The process device of claim 1, wherein the process device is configured for use in a safety instrumented system. 7. The process device of claim 1, wherein the process device is powered entirely by power received through a process control loop. 8. The process device of claim 1, wherein the process control loop is based on

Protocol operation. 9. The process device of claim 1, wherein the diagnostic conditions relate to standardized diagnostic conditions that are mapped to specific current levels. 10. The process device of claim 1, wherein the second process control loop, the second process control loop comprising a second output configured to connect to a second two-wire process control loop, The second output is related to the sensed process variable. 11. The process device of claim 10, wherein the circuitry of the process device is powered entirely by power received through the second process control loop. 12. The process device of claim 10, wherein circuitry associated with at least one of the output and the second output is configured to be powered down during periods of inactivity. 13. The process device of claim 1, wherein the diagnostic circuit is implemented in a feature module connected to a sensor module of the process device. 14. The process device of claim 1, wherein the analog current output changes between the values over time in a predetermined pattern indicative of a diagnostic condition. 15. The process device of claim 1, wherein the analog current level comprises a semi-continuous value. 16. A process device for connection to a two-wire process control loop comprising: diagnostic circuitry configured to diagnose operation of a process device or process; an output configured to connect to a two-wire process control loop configured to provide an analog current output on the loop, wherein the analog current level has a first value indicative of a first diagnostic condition, A second value indicative of the second diagnostic condition and a third value indicative of the third diagnostic condition have a value between 4 milliamperes and 20 milliamperes. 17. The process device of claim 16, wherein the loop analog current output is indicative of more than two diagnostic conditions. 18. The process device of claim 16, wherein the loop analog current output is indicative of predicted diagnostic information. 19. The process device of claim 16, wherein the process device comprises a process variable transmitter. 20. The process device of claim 16, wherein the process device comprises a process controller. 21. The process device of claim 16, wherein the process device is configured for use in a safety instrumented system. 22. The process device of claim 16, wherein the process device is powered entirely by power received through a process control loop. 23. The process device of claim 16, wherein the process control loop is based on

Protocol operation. 24. The process device of claim 16, wherein the diagnostic conditions relate to standard diagnostic conditions that map to specific current levels. 25. The process device of claim 16, wherein the device includes a second process control loop including a second output configured to connect to a second two-wire The process control loop, the second output is related to the sensed process variable. 26. The process device of claim 25, wherein the circuitry of the process device is powered entirely by power received through the second process control loop. 27. The process device of claim 25, wherein circuitry associated with at least one of the output and the second output is configured to de-energize during periods of inactivity. 28. The process device of claim 16, wherein the diagnostic circuit is implemented in a feature module connected to a sensor module of the process device. 29. The process device of claim 16, wherein the analog current output changes between the values over time in a predetermined pattern indicative of a diagnostic condition. 30. The process device of claim 16, wherein the analog current level comprises a semi-continuous value. 31. A process device for connection to a two-wire process control loop comprising: diagnostic circuitry configured to diagnose operation of a process device or process; an output configured to connect to a two-wire process control loop configured to provide an analog current output on the loop, wherein the analog current level has a first value indicative of a first diagnostic condition, A second value indicative of a second diagnostic condition and a third value indicative of a third diagnostic condition, wherein each said value indicates a different predicted diagnostic information. 32. The process device of claim 31, wherein the loop analog current output is between 4 mA and 20 mA. 33. The process device of claim 31, wherein the process device is a process variable transmitter. 34. The process device of claim 31, wherein the process device is a process controller. 35. The process device of claim 31, wherein the process device is configured for use in a safety instrumented system. 36. The process device of claim 31, wherein the process device is powered entirely by electrical power received through a process control loop. 37. The process device of claim 31 , wherein the process control loop is based on The protocol runs. 38. The process device of claim 31, wherein the diagnostic conditions relate to standard diagnostic conditions that are mapped to specific current levels. 39. The process device of claim 31 , wherein the device includes a second process control loop including a second output configured to connect to a second two-wire The process control loop, the second output is related to the sensed process variable. 40. The process device of claim 31, wherein circuitry of the process device is powered entirely by power received through the second process control loop. 41. The process device of claim 31, wherein circuitry associated with at least one of the output and the second output is configured to be powered down during periods of inactivity. 42. The process device of claim 41, wherein the circuitry of the process device is powered entirely by power received from a two-wire process control loop. 43. The process device of claim 31, wherein the diagnostic circuit is implemented in a feature module connected to a sensor module of the process device. 44. The process device of claim 31, wherein the analog current output changes between the values over time in a predetermined pattern indicative of a diagnostic condition. 45. The process device of claim 31, wherein the analog current level comprises a semi-continuous value. 46. A method of notifying diagnostic information associated with a process device or process connected to a two-wire process control loop, the method comprising the steps of: Diagnose the operation of a process plant or process; Outputting an analog current level on a two-wire process control loop, wherein the analog current level has a first value indicative of a first diagnostic condition, a second value indicative of a second diagnostic condition, and a third value indicative of a third diagnostic condition .

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